• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.655-660
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• 2000

This paper presents the construction of consistent coefficient matrix elements for jointed structures using the reduction of flexibility and mass matrices. The reduced flexibility coefficient matrix hat little structural complexity than Guyan's stiffness matrix reduction since the only element of the original matrix, corresponding to the selected nodal degrees of freedom, contributes. The proposed method was applied to building equivalent coefficient matrices for a clamp jointed structure in finite element modal analysis of a cantilevered beam. The theoretical analysis results were compared with those experimental modal analysis, Comparison of both shows good agreement each other.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.533-538
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• 1991

In the design and operation of robot arms with flexible links, the equations of motion are required to exactly model the interaction between rigid motion and elastic motion and to be formulated efficiently. Thus, the flexible link is represented on the basis of the D-H rigid link representation to measure the elastic deformation. The equations of motion of robot arms, which are configured by the generalized coordinates of elastic and rigid degrees of freedom, are formulated by using F.E.M. to model complex shaped links systematically and by eliminating elastic mode of higher order that does not largely affect motion to reduce the number of elastic degree of freedom. Finally, presented is the result of simulation to flexible robotic arm whose joints are controlled by direct or PD control,

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.831-836
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• 1994

This paper presents rational modeling and analysis method for complex structures with various structural joints. For modeling of structural joint, a general modeling technique is newly proposed by flexibility influence coefficient and inverse of flexibility matrix and static reduction concept which is applied to the retained DOFs(degrees of freedom) of detailed finite element model of struction joints. By this method,joint model with contact surface. which can not be reduced by the general reduction theory such as Guyan reduction theory ,can be reduced effectively. And in this method, the nonlinearity of the contact surface can be linearized within a proper range and the boundary effects of joint region can be excluded. Using the proposed method, screwed joint,glued joint and bolted joint are analyzed. And the effectiveness of the proposed method is verified by experiments.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.764-765
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• 2011

In this paper, rotordynamic analyses of the Campbell diagram, critical speeds, and harmonic responses for a TMP rotor system are performed. Since the finite element model of the TMP rotor system has a very large number of degrees of freedom because of its complex geometry, and dynamic analyses for investigating the critical speeds, stability, and harmonic response are repeated for various design parameters, model order reduction (MOR) is necessary to reduce the computational cost. The Krylov-based model order reduction via moment matching significantly speeds up the rotordynamic analyses for the TMP rotor system.

• Structural Monitoring and Maintenance
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• 제5권3호
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• pp.417-428
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• 2018

In this paper, various model reduction methods were assessed using a shear frame, plane and space truss structures. Each of the structures is one-dimensional, two-dimensional and three-dimensional, respectively. Three scenarios of poor, better, and the best were considered for each of the structures in which 25%, 40%, and 60% of the total degrees of freedom (DOFs) were measured in each of them, respectively. Natural frequencies of the full and reduced order structures were compared in each of the numerical examples to assess the performance of model reduction methods. Generally, it was found that system equivalent reduction expansion process (SEREP) provides full accuracy in the model reduction in all of the numerical examples and scenarios. Iterated improved reduced system (IIRS) was the second-best, providing acceptable results and lower error in higher modes in comparison to the improved reduced system (IRS) method. Although the Guyan's method has very low levels of accuracy. Structures were classified with the excitation frequency. High-frequency structures compared to low-frequency structures have been poor performance in the model reduction methods (Guyan, IRS, and IIRS).

• 대한기계학회논문집A
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• 제30권1호
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• pp.18-25
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• 2006

The purpose of this research work is to demonstrate a successful application of hybrid-mixed formulation and nodeless degrees of freedom in developing a very accurate in-plane curved beam element for free vibration analysis. To resolve the numerical difficulties due to the spurious constraints, the present element, based on the Hellinger-Reissner variational principle and considering the effect of shear deformation, employed consistent stress parameters corresponding to cubic displacement polynomials with additional nodeless degrees. The stress parameters were eliminated by the stationary condition, and the nodeless degrees were condensed by Guyan Reduction. Several numerical examples indicated that the property of the mass matrix as well as that of the stiffness matrix have a great effect on the numerical performance. The element with consistent mass matrix produced best results on convergence and accuracy in the numerical analysis of Eigenvalue problems. Also, the higher-order mixed curved beam element showed a superior numerical behavior for the free vibration analyses.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.443-444
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• 2011

This paper discusses a model order reduction for large order rotor dynamics systems results from the finite element discretization. Typical rotor systems consist of a rotor, built-on parts, and a support system, and require prudent consideration in their dynamic analysis models because they include unsymmetric stiffness, localized nonproportional damping and frequency dependent gyroscopic effects. When the finite element model has a very large number of degrees of freedom because of complex geometry, repeated dynamic analyses to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to finish within a practical design cycle. In this paper, the Krylov-based model order reduction via moment matching significantly speeds up the dynamic analyses necessary to check eigenvalues and critical speeds of a Nelson-Vaugh rotor system. With this approach the dynamic simulation is efficiently repeated via a reduced system by changing a running rotational speed because it can be preserved as a parameter in the process of model reduction. The Campbell diagram by the reduced system shows very good agreement with that of the original system. A 3-D finite element model of the Nelson-Vaugh rotor system is taken as a numerical example to demonstrate the advantages of this model reduction for rotor dynamic simulation.

• Journal of Advanced Marine Engineering and Technology
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• 제27권4호
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• pp.520-525
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• 2003

This article provides a dynamic modeling methodology of engines to be accurate with a small number of degrees of freedom for an active vibration control using a top bracing. First. a finite element (FE) model for the engine structure is constructed so that the size of model is as small as possible where the dynamic characteristics of engine are ensured. Second. a technique is studied to obtain the exact mass and stiffness matrices of the FE model. The size of matrices from the FE model is still too large to apply. Finally, a model reduction is. therefore. conducted to make an appropriate dynamic model for designing and simulating a top bracing. In this article, a dynamic model of a large 9 cylinder engine is constructed and reviewed by comparing its natural frequencies and steady state reponses with those of experimental data provided by manufacturer.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.121-122
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• 2006

In the case of mechanical control systems, it is highly useful to be able to provide a compact model of the mechanical system to control engineers using the smallest number of variables, while still providing an accurate model. The reduced mechanical model can then be inserted into the complete mechanical control system models and used for system-level dynamic simulation. In this paper, a moment-matching based model order reduction (MOR) which reduces the number of degrees of freedom of an original finite element model via the Arnoldi process is considered to study the dynamic responses of a HDD actuator and suspension system.

• 산업기술연구
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• 제22권B호
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• pp.251-260
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• 2002

In this thesis, a three degrees of freedom robot, which is able to provide sufficient precision for various robot researches, has been developed. The cable mechanism is used as a basic transmission of robot joints. Based on an optimal design strategy, link and joint parameters are determined and then overall geometry of the robot is designed. As an architecture of robot control, real time control system using real time linux and RtiC-Lab(Real Time Controls Laboratory) is developed. This system, written in C and based on Linux O/S, includes text editor, compiler, downloader, and real time plotter running in host computer for developing control purpose. Using these hardware and software, simple PD position control is implemented, the results shows the effectiveness of the system.